Fixes for creating and updating Hipchat users

While using the HypChat library I bumped into a few problems:
- User.save() worked but raised an exception on return
- commit 8dee52b84ae32448e15a4df72a7890aaac76bcf1 broke HypChat.create_user()
- the default parameters of HypChat.create_user() collide with the API

With these commits they are all fixed.